Multicolor holgraphic replication by masking

ABSTRACT

A multicolor hologram (e.g., a two-color hologram) is replicated (copied) into a photosensitive layer by masking to produce a copy (replicate) of the hologram in a manner such that the copy is an accurate and true replication of the hologram (e.g., master hologram) and the copy is characterized to possess a high brightness level and color fidelity comparable to that of the multicolor hologram that was replicated. Both flood and scan modes can be employed in the replication.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 from U.S.Provisional Application Ser. No. 60/910,272 (filed Apr. 5, 2007), thedisclosure of which is incorporated by reference herein for all purposesas if fully set forth. This application is a continuation of U.S. patentapplication Ser. No. 12/080,620, filed on Apr. 4, 2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to a method for replicating (copying) amulticolor hologram (e.g., a two-color hologram) into a photosensitivelayer by masking to produce a copy (replicate) of the hologram in amanner such that the copy is an accurate and true replication of thehologram (e.g., master hologram) and the copy is characterized topossess a high brightness level and good color fidelity/puritycomparable to that of the hologram that was replicated.

2. Description of Related Art

Replication by direct contact copying of a master hologram (either areflection hologram or a transmission hologram) in which the masterhologram is in direct contact with a photosensitive layer (e.g., aholographic recording film) is known from the art. With respect toreflection holograms, see, for example, the following references: 1)“Improved Process of Reflection Holography Replication and HeatProcessing”, by D. F. Tipton, M. L. Armstrong, and S. H. Stevenson,Proc. SPIE, Vol. 2176, p 172-183 in Practical Holography VIII, StephenA. Benton, Ed.; 2) “Photographic Reconstruction of the OpticalProperties of an Object in its Own Scattered Radiation Field”, by Yu N.Denisyuk, Soviet Physics—Doklady, 7, pages 543-5 (1962); and 3) “CopyingReflection Holograms”, by Clark N. Kurtz, Journal of the Optical Societyof America, 58, pages 856-7 (1968); each of these open literaturereferences is incorporated by reference. Pertinent references in thepatent literature include U.S. Pat. Nos. 4,995,685; 6,824,929; and6,097,514, which are incorporated by reference. With respect totransmission holograms, see, for example, U.S. Pat. No. 4,209,250, whichdiscloses a system for making multiple copies from a stationary planartransmission master hologram, and U.S. Pat. No. 4,973,113, whichdescribes a method and apparatus for making a copy of a transmissionhologram from a master. An additional open literature reference thatcovers copying of both reflection and transmission holograms is thereplication portions of Chapter 20 of Optical Holography by R. J.Collier, C. B. Burchhardt and L. H. Lin, Academic Press (1971), which isincorporated by reference. The prior art teaches that such directcontact copying is done by contacting a photosensitive element,comprised of a photosensitive layer and a smooth coversheet, to a smoothmaster hologram such that a smooth surface of the coversheet is indirect contact with a smooth surface of the master hologram. It has beenfound that a method to make a multicolor hologram was needed. Thepresent invention describes such a method.

SUMMARY OF THE INVENTION

In an embodiment, the invention is a method for replicating a volumereflection master hologram comprising:

-   -   a) providing a photosensitive layer having a side and an        opposing side;    -   b) placing the side of the photosensitive layer in contact with        or proximate to the master hologram;    -   c) placing a first mask in contact with or proximate to the        opposing side of the photosensitive layer masking at least one        area of the photosensitive layer;    -   d) exposing the photosensitive layer through the first mask with        coherent actinic radiation of a first wavelength λ₁ resulting in        a first wavelength exposed layer;    -   e) removing the first mask; and    -   f) exposing the first wavelength exposed layer with coherent        actinic radiation of a second wavelength λ₂ resulting in a first        and second wavelength exposed layer, wherein the first and        second wavelength exposed layer is a replicate of the volume        reflection master hologram.

In another embodiment, the invention is a method for replicating avolume reflection master hologram comprising:

-   -   a) providing a photosensitive layer having a side and an        opposing side;    -   b) placing the side of the photosensitive layer in contact with        or proximate to the master hologram;    -   c) placing a first mask in contact with or proximate to the        opposing side of the photosensitive layer masking at least one        area of the photosensitive layer;    -   d) exposing the photosensitive layer through the first mask with        coherent actinic radiation of the first wavelength λ₁ resulting        in a first wavelength exposed layer;    -   e) removing the first mask;    -   f) placing a second mask in contact with or proximate to the        opposing side of the photosensitive layer that is now the first        wavelength exposed layer masking at least one area of the first        wavelength exposed layer;    -   g) exposing the first wavelength exposed layer with coherent        actinic radiation of a second wavelength λ₂ resulting in a first        and second wavelength exposed layer;    -   h) removing the second mask; and    -   i) exposing the first and second wavelength exposed layer with        coherent actinic radiation of a third wavelength λ₃ resulting in        a first, second and third wavelength exposed layer, wherein the        first, second and third wavelength exposed layer is a replicate        of the volume reflection master hologram.

In an embodiment, the invention is a method for replicating a volumereflection master hologram comprising:

-   -   a) providing a photosensitive layer having a side and an        opposing side;    -   b) placing the side of the photosensitive layer in contact with        or proximate to the master hologram;    -   c) placing a first mask in contact with or proximate to the        opposing side of the photosensitive layer masking at least one        area of the photosensitive layer;    -   d) exposing the photosensitive layer through the first mask with        coherent actinic radiation of the first wavelength λ₁ resulting        in a first wavelength exposed layer;    -   e) removing the first mask;    -   f) placing a second mask in contact with or proximate to the        opposing side of the photosensitive layer that is now the first        wavelength exposed layer masking at least one area of the first        wavelength exposed layer;    -   g) exposing the first wavelength exposed layer with coherent        actinic radiation of a second wavelength λ₂ resulting in a first        and second wavelength exposed layer;    -   h) removing the second mask;    -   i) placing a third mask in contact with or proximate to the        opposing side of the photosensitive layer that is now the first        and second wavelength exposed layer masking at least one area of        the photosensitive layer;    -   j) exposing the first and second wavelength exposed layer with        coherent actinic radiation of a third wavelength λ₃ resulting in        a first, second and third wavelength exposed layer;    -   k) removing the third mask; and    -   l) exposing the first, second and third wavelength exposed layer        with coherent actinic radiation of a fourth wavelength λ₄        resulting in a first, second, third, and fourth wavelength        exposed layer, wherein the first, second, third, and fourth        wavelength exposed layer is a replicate of the volume reflection        master hologram.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates a side view of an assembly of key components formasked replication according to an embodiment of the invention. Aphotosensitive layer 1, which has a side 2 and an opposing side 3, isprovided. The side 2 is placed in contact with or proximate to a volumereflection master hologram 4. A mask 5 having one or more unmaskedarea(s) 6 is placed in contact with or proximate to the opposing side 3of the photosensitive layer 1 masking at least one area of thephotosensitive layer 1. The photosensitive layer 1 is then exposed tocoherent actinic radiation of a first wavelength λ₁ through the mask. Asis indicated with arrows in FIG. 1, light rays incident upon unmaskedarea(s) 6 are transmitted through the mask 5 to the master hologram 4while those light rays incident upon masked area(s) are prevented fromreaching the photosensitive layer 1 and the master hologram 4 by themask. After this first exposure, the first mask is removed. Inembodiments, a second mask is placed where the first mask had beenpositioned earlier (during the first exposure) prior to the secondexposure being done. After the second exposure has been completed, thesecond mask is removed and then a third mask optionally is placed wherethe first and second masks had been positioned earlier (during the firstand second exposures, respectively) prior to the third exposure beingdone. The third exposure may be done without a third mask.

DETAILED DESCRIPTION

This invention in various embodiments is method(s) for replicatingefficiently multi-color (e.g., two-color, three-color, four-color)volume reflection holograms. The resulting holograms replicatedaccording to this invention are characterized to possess high brightnesslevels and better color fidelity in relation to similar holograms thatare replicated according to prior art replication methods. Thisinvention entails use of a mask(s) (e.g., first and second masks) and aphotosensitive layer to replicate a multi-color volume reflection masterhologram within the photosensitive layer.

FIG. 1 illustrates a side view of an assembly of key components formasked replication according to an embodiment of the invention. Aphotosensitive layer 1, which has a side 2 and an opposing side 3, isprovided. The side 2 is placed in contact with or proximate to a volumereflection master hologram 4. A mask 5 (e.g., initially a first mask andoptionally, later a second mask) having one or more unmasked area(s) 6is placed in contact with or proximate to the opposing side 3 of thephotosensitive layer 1 masking at least one area of the photosensitivelayer 1. The photosensitive layer 1 is then exposed to coherent actinicradiation of a first wavelength λ₁ through the mask. As is indicatedwith arrows in FIG. 1, light rays incident upon unmasked area(s) 6 aretransmitted through the mask 5 to the master hologram 4 while thoselight rays incident upon masked area(s) are prevented from reaching thephotosensitive layer 1 and the master hologram 4 by the mask. After thisfirst exposure, the first mask is removed. In an embodiment, a secondexposure is then done with coherent actinic radiation of wavelength λ₂without using a second mask. In another embodiment, a second mask isplaced where the first mask had been positioned earlier (during thefirst exposure) prior to the second exposure being done.

The multi-color master volume reflection holograms employed as mastersand to be replicated according to this invention can be made of anysuitable photosensitive material capable of recording a holographicimage, including, but not limited to, dichromated gelatin (DCG) andphotopolymer. In an embodiment, DCG is the photosensitive material usedin making a master hologram to be used in subsequent replication.

The photosensitive layer used according to the invention to recordholographic replicates can be made of any suitable photosensitivematerial capable of recording a holographic image, including, but notlimited to, photopolymer (e.g., holographic recording film),photographic film, and dichromated gelatin (DCG). In an embodiment, thephotosensitive layer is a photopolymer. In one embodiment, thephotopolymer is a holographic recording film (HRF). The HRF may be anOmnidex® HRF (E.I. DuPont de Nemours, Wilmington, Del.).

The first mask and (when present) the second mask can be made of anymaterials that effectively block actinic radiation (e.g., visible light)from passing through the masks in areas that are not to be exposed in agiven exposure and which effectively transmit actinic radiation (e.g.,visible light) in areas that are to be exposed during a given exposure.Suitable masks include, but are not limited to, those made oftransparent polymers (e.g., polyester) that effectively transmit actinicradiation of the desired wavelengths in areas to be exposed and whichare coated in areas to be blocked with absorptive material(s) (e.g., ablack ink) that effectively blocks actinic radiation in coated areaswhere blocking is desired to prevent exposure to actinic radiation.

In the methods according to the invention, the photosensitive layerhaving a side and an opposing side is placed between the master hologramand the mask (e.g., first mask). The master hologram is usually, but notnecessarily, comprised of a rigid, transparent (e.g., glass) protectivecap. The side of photosensitive layer is usually placed in directcontact with the protective cap of the master hologram (if one ispresent) or in direct contact with a hologram layer of the master (if aprotective cap is absent) in order to achieve optical coupling of thephotosensitive layer to the master hologram and provide for stability ofthe coupled system (master, including protective cap if present, andphotosensitive layer) during holographic imaging. The mask can either bein contact with or proximate to the opposing side of photosensitivelayer. In this invention, the terms “proximate to” with respect to thefirst mask and photosensitive layer means that the opposing side of thephotosensitive layer and a nearest surface of the first mask are spacedwithin 1 mm of each other.

Exposing the photosensitive layer to coherent actinic radiation of afirst wavelength λ₁ is done through a first mask with the first maskmasking at least one area of the photosensitive layer. Any means ofproducing coherent actinic radiation can be employed. In an embodiment,lasers are used. The first wavelength λ₁ can lie in any region of theelectromagnetic spectrum, including, but not limited to, the visibleregion, the infra-red region, and the ultraviolet (UV) region. In oneembodiment, the first wavelength lies in the visible region. A firstwavelength λ₁ exposure transforms the photosensitive layer into a firstwavelength exposed layer.

After the first wavelength exposure has been completed, additional stepsmay include: (1) in one embodiment, the first mask is removed andexposure to a second wavelength λ₂ is done without a mask being inplace; (2) in another embodiment, the first mask is replaced with asecond mask prior to exposure to a second wavelength λ₂.

Exposing the photosensitive layer to coherent actinic radiation of asecond wavelength λ₂ can be done either without a mask or through asecond mask. (This second exposure can be done without a mask sincevirtually all first exposed areas are no longer photosensitive followingthe first exposure at the first wavelength.) Any means of producingcoherent actinic radiation can be employed; lasers are preferred. Thesecond wavelength λ₂ can broadly lie in any region of theelectromagnetic spectrum, including, but not limited to, the visibleregion, the infra-red region, and the ultraviolet (UV) region. In oneembodiment, the second wavelength lies in the visible region. Thissecond wavelength λ₂ exposure, together with the first wavelength λ₁exposure, transforms the photosensitive layer into a first and secondwavelength exposed layer, which is a replicate of the two-color masterhologram.

In an embodiment, coherent actinic radiation of the first wavelength λ₁and coherent actinic radiation of the second wavelength λ₂ are withinthe visible region of the electromagnetic spectrum.

In another embodiment, coherent actinic radiation of the firstwavelength λ₁ and coherent actinic radiation of the second wavelength λ₂are independently selected to correspond to light from the groupconsisting of red light, blue light, and green light with the provisothat light of the first wavelength and light of the second wavelengthcorrespond to different colors.

In another embodiment, coherent actinic radiation of the firstwavelength λ₁ or coherent actinic radiation of the second wavelength λ₂corresponds to blue light and wherein at least one of the firstwavelength exposed layer and the first and second wavelength exposedlayer is color-tuned such that the replicate of the two-color masterhologram plays back in the green region of visible light.

In another embodiment, coherent actinic radiation of the firstwavelength λ₁ or coherent actinic radiation of the second wavelength λ₂corresponds to green light and wherein at least one of the firstwavelength exposed layer and the first and second wavelength exposedlayer is color-tuned such that the replicate of the two-color masterhologram plays back in the red region of visible light.

In the method for replicating a two-color volume reflection masterhologram, the exposing steps (steps d) and f)) can be done in any mannerincluding, but not limited to, exposing in a flood exposure mode or in ascan exposure mode. In case of exposing in a flood exposure mode, theentire layer (photosensitive layer or first wavelength exposed layer)that is being exposed is exposed at the same time to coherent actinicradiation. In case of exposing in a scan exposure mode, only a portionof the entire layer (photosensitive layer or first wavelength exposedlayer) that is being exposed is exposed at the same time to coherentactinic radiation. For example, in the scan mode, a moving beam ofcoherent actinic radiation may be scanned across the entire layer(photosensitive layer or first wavelength exposed layer) over a periodof time to effect the scanned exposure. Typically, a flood exposure isdone with lower power density over a longer period of time in comparisonto a scan exposure.

In general, the relationship between the first wavelength λ₁ and thesecond wavelength λ₂ is not limited. In an embodiment, the absolutevalue of (the first wavelength λ₁ minus the second wavelength λ₂) is atleast 7 nm. In an embodiment, the absolute value of (the firstwavelength λ₁ minus the second wavelength λ₂) is at least 30 nm,preferably at least 40 nm, and more preferably at least 50 nm.

In replication of a two-color hologram, the first mask is designed toeffectively block actinic radiation from all areas targeted to beexposed during the second exposure with the second wavelength actinicradiation and to effectively pass actinic radiation of the firstwavelength in areas targeted to be exposed during the first exposure.The second mask is optional and, if present, is chosen such that it willeffectively block actinic radiation during the second exposure fromreaching areas of the first wavelength exposed layer that werepreviously exposed during the first exposure.

The method for replicating a three-color or four-color volume reflectionhologram according to the invention is similar to the method describedsupra for replicating a two-color volume reflection hologram and thedetails given herein apply equally to two-color, three-color, andfour-color volume reflection holograms except as may be specificallynoted somewhere within this specification. A main difference is that athree-color replication involves three different imaging wavelengths(instead of two different imaging wavelengths) and either two oroptionally three masks are utilized (instead of one or optionally twomasks for two-colors) in replicating a three-color volume reflectionhologram according to the invention. Similarly, a main difference isthat a four-color replication involves four different imagingwavelengths (instead of two or three different imaging wavelengths) andeither three or optionally four masks are utilized (instead of fewermasks for the two-color and three-color cases) in replicating afour-color volume reflection hologram according to the invention.

More specifically, in an embodiment for replicating a three-color volumereflection hologram according to the invention, a photosensitive layeris placed between a master hologram and a first mask. The photosensitivelayer is then exposed through the first mask to coherent actinicradiation of a first wavelength λ₁ resulting in first wavelength exposedlayer. The first mask is removed and replaced (in the same location)with a second mask. The first wavelength exposed layer is then exposedthrough the second mask to coherent actinic radiation of a secondwavelength λ₂ resulting in a first and second wavelength exposed layer.At this point, there are two choices prior to the third exposure. Onechoice is to do the third exposure without a (third) mask being present,and the other choice is to employ a third mask during the thirdexposure. If a third mask is employed, it is placed in the same locationas the first and second masks were located earlier according to themethod. With either choice, the first and second wavelength exposedlayer is next exposed to coherent actinic radiation of a thirdwavelength λ₃ resulting in a first, second, and third wavelength exposedlayer, wherein the first, second and third wavelength exposed layer is areplicate of the three-color master hologram.

In replication of a three-color hologram according to the invention, thefirst mask is designed to effectively block actinic radiation from allareas except those targeted to be exposed during the first exposure withthe first wavelength actinic radiation and to effectively pass actinicradiation of the first wavelength in areas targeted to be exposed duringthe first exposure. The second mask is designed to at least effectivelyblock actinic radiation from all areas targeted for the third exposureand to effectively pass actinic radiation from all areas targeted forthe second exposure with the second wavelength actinic radiation. Thethird mask is optional and, if employed, is usually designed to blockactinic radiation from all areas except those targeted for the thirdexposure with the third wavelength actinic radiation; the third maskshould effectively pass actinic radiation of the third wavelength inthose areas targeted for exposure with the third wavelength actinicradiation.

In an embodiment for the method for replicating a three-color volumereflection master hologram described supra, the absolute values ofλ₁-λ₂, λ₁-λ₃, and λ₂-λ₃ are each at least 7 nm. In another embodiment,the absolute values of λ₁-λ₂, λ₁-λ₃, and λ₂-λ₃ are each at least 30 nm,preferably at least 40 nm, and more preferably at least 50 nm. Inanother embodiment, the at least one area masked in step c) is alsomasked in step f).

More specifically, in an embodiment for replicating a four-color volumereflection hologram according to the invention, a photosensitive layeris placed between a master hologram and a first mask. The photosensitivelayer is then exposed through the first mask to coherent actinicradiation of a first wavelength λ₁ resulting in first wavelength exposedlayer. The first mask is removed and replaced (in the same location)with a second mask. The first wavelength exposed layer is then exposedthrough the second mask to coherent actinic radiation of a secondwavelength λ₂ resulting in a first and second wavelength exposed layer.The second mask is removed and replaced (in the same location) with athird mask. The first and second wavelength exposed layer is thenexposed through the third mask to coherent actinic radiation of a thirdwavelength λ₃ resulting in a first, second, and third wavelength exposedlayer. At this point, there are two choices prior to the fourthexposure. One choice is to do the fourth exposure without a (fourth)mask, and the other choice is to employ a fourth mask during the fourthexposure. With either choice, the first, second, and third wavelengthexposed layer is next exposed to coherent actinic radiation of a fourthwavelength λ₄ resulting in a first, second, third, and fourth wavelengthexposed layer, wherein the first, second, third, and fourth wavelengthexposed layer is a replicate of the four-color master hologram.

In an embodiment for a method of replicating a four-color volumereflection master hologram as described supra, the absolute values ofλ₁-λ₂, λ₁-λ₃, λ₁-λ₄, λ₂-λ₃, λ₂-λ₄, and λ₃-λ₄ are each at least 7 nm. Inanother embodiment, the absolute values of λ₁-λ₂, λ₁-λ₃, λ₁-λ₄, λ₂-λ₃,λ₂-λ₄, and λ₃-λ₄ are each at least 30 nm, preferably at least 40 nm, andmore preferably at least 50 nm. In another embodiment, the at least onearea masked in step c) is also masked in steps f) and l).

In a preferred embodiment of a multi-color replication method accordingto the invention, the first mask blocks actinic radiation from exposingthe greatest percentage surface area of the film available for exposurein the (initially) photosensitive film and the percentage of surfacearea blocked decreases in the order of second mask, third mask (whenpresent), and fourth mask (when present). Such blockage preventspremature exposure and deactivation/interference in areas targeted for alater exposure (e.g., prevents exposure during exposing steps with firstand second wavelengths in areas targeted for exposure with a thirdwavelength). As one example of this preferred embodiment for athree-color replication, the first mask should effectively block actinicradiation of the second and third wavelengths while effectively passingactinic radiation of the first wavelength. The second mask should at aminimum effectively block actinic radiation of the third wavelengthwhile effectively passing actinic radiation of the second wavelength.

EXAMPLES Example 1

This example illustrates replication of a full chuck of two-color masterholograms into holographic recording film (a photopolymer) using atwo-color masked sequential flood process according to the invention.The following process steps for replication were conducted in the orderas listed.

-   -   1) A full master chuck of H2 masters was assembled. The full        master chuck was of dimensions 12 inches×18 inches. Each H2        master was 2 inches×2 inches and there were 54 masters in the        full chuck. Each H2 master was made by H1-H2 holographic imaging        with lasers in dichromated gelatin (DCG) using a well-known        method (see Y. Denisyuk, Optical Holography, R. J. Collier et        al., Academic Press, 1971, especially paragraph 3 on pages        21-22) together with color tuning of exposed and wet processed        DCG to lower the playback wavelength to a desired point as is        well-known in the art. Each master contained areas that played        back at either of two distinct wavelengths—one at a blue        wavelength and one at a green wavelength.    -   2) A polyester mask was made that covered the master chuck        allowing laser light to penetrate only in designated areas of        each H2 master. The mask was designed such that the vast        majority was black. This corresponded with the intent to produce        a two-color image that was mostly green after color tuning. The        two-color image had only small red areas following color tuning.        The small clear areas on the mask correspond to what became red        areas in the two-color image. The mask was computer generated        and sent to an image setter (Agfa Select Set 7000). The image        setter functioned such that polyester passed through an        emulsification process in this device to produce black areas of        the mask.    -   3) Photopolymer (DuPont 734-1 Holographic Recording Film        (HRF), E. I. DuPont de Nemours, Wilmington, Del.) was vacuum        coupled to the surface of the master chuck, after which time the        polyester mask was overlaid and vacuum coupled to the surface of        the HRF. The mask used was one containing clear areas that        transmit visible light and opaque areas that block visible        light. Both layers were rolled down to ensure complete coupling.    -   4) The entire master chuck was then flood exposed with 532 nm        laser light for a predetermined period of time of 25 seconds        that resulted in an exposure level of 50 mJ/cm2. Only the clear        areas of the polyester mask allowed for penetration of the laser        light. Since these clear areas of the mask were registered to        the areas of the master that play back at 532 nm, all clear        areas resulted in 532 nm images.    -   5) The mask was then removed from the master chuck while the HRF        film was kept in place. Once the mask was removed, the entire        master chuck was flood exposed with 476 nm laser light for a        time of 25 seconds that resulted in an exposure level of 25        mJ/cm2. The previously exposed 532 nm portions remained        unaffected by the additional 476 nm exposure as complete        polymerization had already occurred during the 532 nm exposure        such that these exposed 532 nm portions were no longer        photosensitive.    -   6) The 476 nm and 532 nm exposed HRF that resulted at the end of        step 5) was immediately exposed to UV light to prevent any        incidental color shifting resulting from ambient light exposure.        The approximate ranges for power and exposure time for this step        were 6-12 milliwatts and 30-70 seconds, respectively.    -   7) Following step 6), the exposed HRF was then laminated to 146        Color Tuning Film (CTF) (E. I. DuPont de Nemours, Wilmington,        Del.) using a DuPont laminator (E.I. DuPont de Nemours,        Wilmington, Del.) operated at a speed of 3.0 m/min and a        temperature of 100° C.    -   8) The combined HRF/CTF from step 7) was then heated for 7        minutes at 150° C. to afford a true and stable volume hologram        replicate of the original full H2 master chuck in the        photopolymer (exposed and color-tuned HRF) that has been        color-tuned such that the imaged portions that were initially        blue now play-back as green image portions at approximately        530-550 nm and such that the imaged portions that were initially        green now play-back as red image portions at approximately        600-610 nm.

Both of the final green and red image portions of the replicatedhologram were characterized to be bright and have good color purity.

Example 2

This example illustrates replication of a full chuck of two-color masterholograms into holographic recording film (a photopolymer) using atwo-color masked sequential scan process according to the invention. Thefollowing process steps for replication were conducted in the order aslisted.

-   -   1) A full master chuck of H2 masters was assembled. The full        master chuck was of dimensions 12 inches×18 inches. Each H2        master was 2 inches×2 inches and there were 54 masters in the        full chuck. Each H2 master was made by H1-H2 holographic imaging        with lasers in dichromated gelatin (DCG) using a well-known        method (see Y. Denisyuk, Optical Holography, R. J. Collier et        al., Academic Press, 1971, especially paragraph 3 on pages        21-22) together with color tuning of exposed and wet processed        DCG to lower the playback wavelength to a desired point as is        well-known in the art. Each master contained areas that played        back at either of two distinct wavelengths—one at a blue        wavelength and one at a green wavelength.    -   2) A polyester mask was made that covered the master chuck        allowing laser light to penetrate only in designated areas of        each H2 master. The mask was designed such that the vast        majority was black. This corresponded with the intent to produce        a two-color image that was mostly green after color tuning. The        two-color image had only small red areas following color tuning.        The small clear areas on the mask correspond to what became red        areas in the two-color image. The mask was computer generated        and sent to an image setter (Agfa Select Set 7000). The image        setter functioned such that polyester passed through an        emulsification process in this device to produce black areas of        the mask.    -   3) Photopolymer (DuPont 734-1 Holographic Recording Film        (HRF), E. I. DuPont de Nemours, Wilmington, Del.) was vacuum        coupled to the surface of the master chuck, after which time the        polyester mask was overlaid and vacuum coupled to the surface of        the HRF. The mask used was one containing clear areas that        transmit visible light and opaque areas that block visible        light. Both layers were rolled down to ensure complete coupling.    -   4) The entire master chuck was then line scanned with a 532 nm        laser beam measuring approximately ⅜ inch×20 inches at a        predetermined speed of ⅜ inch per second that resulted in an        exposure level of 50 mJ/cm2. The scan time was 33 seconds. Only        the clear areas of the polyester mask allowed for penetration of        the laser light. Since the entirety of each H2 master was        covered with a 532 nm reflector, all clear areas resulted in 532        nm images.    -   5) The mask was then removed from the master chuck while the HRF        film was kept in place. Once the mask was removed, the entire        master chuck was line scanned with a 476 nm laser beam measuring        approximately ⅜ inch×20 inches at a predetermined speed of ⅜        inch per second that resulted in an exposure level of 25 mJ/cm2.        The scan time was 33 seconds. The previously exposed 532 nm        portions remained unaffected by the additional 476 nm exposure        as complete polymerization had already occurred during the 532        nm exposure such that these exposed 532 nm portions were no        longer photosensitive.    -   6) The 476 nm and 532 nm exposed HRF that resulted at the end of        step 5) was immediately exposed to UV light to prevent any        incidental color shifting resulting from ambient light exposure.        The approximate ranges for power and exposure time for this step        were 6-12 milliwatts and 30-70 seconds, respectively.    -   7) Following step 6), the exposed HRF was then laminated to 146        Color Tuning Film (CTF) (E. I. DuPont de Nemours, Wilmington,        Del.) using a DuPont laminator (E.I. DuPont de Nemours,        Wilmington, Del.) operated at a speed of 3.0 m/min and a        temperature of 100° C.    -   8) The combined HRF/CTF from step 7) was then heated for 7        minutes at 150° C. to afford a true and stable volume hologram        replicate of the original full H2 master chuck in the        photopolymer (exposed and color-tuned HRF) that has been        color-tuned such that the imaged portions that were initially        blue now play-back as green image portions at approximately        530-550 nm and such that the imaged portions that were initially        green now play-back as red image portions at approximately        600-610 nm.

Both of the final green and red image portions of the replicatedhologram were characterized to be bright and have good color purity.

Example 3 Comparative

This comparative example illustrates replication of a full chuck oftwo-color master holograms into holographic recording film (aphotopolymer) using a two-color simultaneous flood process without amask as known and practiced in the prior art. The following processsteps for replication were conducted in the order as listed.

-   -   1) A full master chuck of H2 masters was assembled. The full        master chuck was of dimensions 12 inches×18 inches. Each H2        master was 2 inches×2 inches and there were 54 masters in the        full chuck. Each H2 master was made by H1-H2 holographic imaging        with lasers in dichromated gelatin (DCG) using a well-known        method (see Y. Denisyuk, Optical Holography, R. J. Collier et        al., Academic Press, 1971, especially paragraph 3 on pages        21-22) together with color tuning of exposed and wet processed        DCG to lower the playback wavelength to a desired point as is        well-known in the art. Each master contained areas that played        back at either of two distinct wavelengths—one at a blue        wavelength and one at a green wavelength.    -   2) Photopolymer (DuPont 734-1 Holographic Recording Film        (HRF), E. I. DuPont de Nemours, Wilmington, Del.) was vacuum        coupled to the surface of the master chuck. The photopolymer        layer was rolled down to ensure complete coupling.    -   3) The entire master chuck was then simultaneously flood exposed        to both 532 nm and 476 nm laser light for a predetermined period        of time of 40 seconds that resulted in an exposure level of 50        mJ/cm2 of 532 nm light and 25 mJ/cm2 of 476 nm light.    -   4) The 476 nm and 532 nm exposed HRF that resulted at the end of        step 3) was immediately exposed to UV light to prevent any        incidental color shifting resulting from ambient light exposure.        The approximate ranges for power and exposure time for this step        were 6-12 milliwatts and 30-70 seconds, respectively.    -   5) Following step 4), the exposed HRF was then laminated to 146        Color Tuning Film (CTF) (E. I. DuPont de Nemours, Wilmington,        Del.) using a DuPont laminator (E.I. DuPont de Nemours,        Wilmington, Del.) operated at a speed of 3.0 m/min and a        temperature of 100° C.    -   6) The combined HRF/CTF from step 5) was then heated for 7        minutes at 150° C. to afford a stable volume hologram replicate        of the original full H2 master chuck in the photopolymer        (exposed and color-tuned HRF) that has been color-tuned such        that the imaged portions that were initially blue now play-back        mainly as green image portions at approximately 530-550 nm and        such that the imaged portions that were initially green now        play-back mainly as red image portions at approximately 600-610        nm.

Although the process of this comparative example affords a stable volumehologram, the hologram obtained has very significant drawbacks relativeto those holograms obtained with the inventive processes of Examples 1and 2. These drawbacks are that the hologram obtained using the processof this Comparative Example 3 has significantly lower brightness andalso poorer color purity and color contrast characteristics incomparison to the holograms obtained using the inventive processes asgiven in Examples 1 and 2. Colors produced under the inventive methodare also purer because the viewer isn't seeing two colors at once. Whilenot being bound by theory, the inventors believe that the lowerbrightness characteristics of the hologram of this comparative exampleare due to detrimental effects of the simultaneous presence of the 476nm and 532 nm beams during holographic imaging competing for availabledifferences in refractive index between the unexposed and exposedphotosensitive film (e.g., HRF). This is because even though a certainarea of the H2 was intended to only playback at a single wavelength,there is still a small amount of light from the unintended wavelengthreflecting off that area. As mentioned above, this unintended wavelengthis competing for limited available differences in refractive index andthus not leaving it entirely available for the intended wavelength. Thissharing of the refractive index results in the intended wavelengthappearing more dim and also less pure as the area is not simplyreflecting a single wavelength.

1. A method for replicating a volume reflection master hologramcomprising, in sequence as listed below: a) providing a photosensitivelayer having a side and an opposing side, b) placing the side of thephotosensitive layer in contact with or proximate to the masterhologram; c) placing a first mask in contact with or proximate to theopposing side of the photosensitive layer masking at least one area ofthe photosensitive layer; d) exposing the photosensitive layer throughthe first mask with coherent actinic radiation of a first wavelength λ₁resulting in a first wavelength exposed layer; e) removing the firstmask; f) placing a second mask in contact with or proximate to theopposing side of the photosensitive layer that is now the firstwavelength exposed layer masking at least one area of the firstwavelength exposed layer; g) exposing the first wavelength exposed layerwith coherent actinic radiation of a second wavelength λ₂ resulting in afirst and second wavelength exposed layer; h) removing the second mask;and i) exposing the first and second wavelength exposed layer withcoherent actinic radiation of a third wavelength λ₃ resulting in afirst, second and third wavelength exposed layer, wherein the first,second and third wavelength exposed layer is a replicate of the volumereflection master hologram.
 2. The method of claim 1 wherein, afterexposing the second mask to the coherent actinic radiation, the secondmask is replaced with a third mask prior to i) being executed.
 3. Themethod of claim 2 wherein the second mask is chosen such that it willeffectively block actinic radiation during the second exposure fromreaching areas of the first wavelength exposed layer that werepreviously exposed during the first exposure.
 4. The method of claim 1wherein coherent actinic radiation of the first wavelength λ₁, coherentactinic radiation of the second wavelength λ₂, and coherent actinicradiation of the third wavelength λ₃ are within a visible region of theelectromagnetic spectrum.
 5. The method of claim 1 wherein coherentactinic radiation of the first wavelength λ₁, coherent actinic radiationof the second wavelength λ₂, or coherent actinic radiation of the thirdwavelength λ₃ corresponds to blue light and wherein at least one of thefirst wavelength exposed layer, the first and second wavelength exposedlayer, and the first, second and third wavelength exposed layer iscolor-tuned such that the replicate of the volume reflection masterhologram plays back in a green region of visible light.
 6. The method ofclaim 1 wherein coherent actinic radiation of the first wavelength λ₁,coherent actinic radiation of the second wavelength λ₂, or coherentactinic radiation of the third wavelength λ₃ corresponds to green lightand wherein at least one of the first wavelength exposed layer, thefirst and second wavelength exposed layer or the first, second, andthird exposed layer is color-tuned such that the replicate of thetwo-color master hologram plays back in a red region of visible light.7. The method of claim 1 wherein the photosensitive layer is aphotopolymer.
 8. The method of claim 7 wherein the photopolymer is aholographic recording film.
 9. The method of claim 1 wherein theexposing steps d) and g) and i) are done in a flood exposure mode. 10.The method of claim 1 wherein the exposing steps d) and g) and i) aredone in a scan exposure mode with a moving beam of coherent actinicradiation.
 11. The method of claim 1 wherein the absolute values ofλ₁-λ₂, λ₁-λ₃, and λ₂-λ₃ are each at least 7 nm.
 12. The method of claim1 wherein the at least one area masked in step c) is also masked in stepf).
 13. The method of claim 1 wherein the placing of the side of thephotosensitive layer is such that the side of the photosensitive layeris in contact with the master hologram.
 14. The method of claim 1wherein the placing of the first mask in c) is such that the first maskis in contact with the opposing side of the photosensitive layer.
 15. Amethod for replicating a volume reflection master hologram comprising:a) providing a photosensitive layer having a side and an opposing side;b) placing the side of the photosensitive layer in contact with orproximate to the master hologram; c) placing a first mask in contactwith or proximate to the opposing side of the photosensitive layermasking at least one area of the photosensitive layer; d) exposing thephotosensitive layer through the first mask with coherent actinicradiation of a first wavelength λ₁ resulting in a first wavelengthexposed layer; e) removing the first mask; f) placing a second mask incontact with or proximate to the opposing side of the photosensitivelayer that is now the first wavelength exposed layer masking at leastone area of the first wavelength exposed layer; g) exposing the firstwavelength exposed layer with coherent actinic radiation of a secondwavelength λ₂ resulting in a first and second wavelength exposed layer;h) removing the second mask; i) placing a third mask in contact with orproximate to the opposing side of the photosensitive layer that is nowthe first and second wavelength exposed layer masking at least one areaof the photosensitive layer; j) exposing the first and second wavelengthexposed layer with coherent actinic radiation of a third wavelength λ₃resulting in a first, second and third wavelength exposed layer; and k)removing the third mask; wherein the first, second, and third wavelengthexposed layer is a replicate of the volume reflection master hologram.16. The method of claim 15 wherein absolute values of λ₁-λ₂, λ₁-λ₃, andλ₂-λ₃ are each at least 7 nm.
 17. The method of claim 15 wherein the atleast one area masked in step c) is also masked in steps f) and i).